Phase-locked loops (PLLs) are a key component in modern IC designs. The PLL can be used in various electrical circuits, such as clock recovery circuits, frequency synthesizers, and frequency and phase modulators. In general, the PLL uses a voltage-controlled oscillator (VCO) to provide an oscillation signal with a desired frequency. The VCO used in the PLL is an LC-tank VCO or a ring-based VCO. The ring-based VCO has a compact size and a wider bandwidth, making the ring-based VCO more popular than the LC-tank VCO in certain types of IC design.